Subjects will be healthy males or females aged 20 to 40 years of age who will be recruited to participate in an MRI scan designed to measure clinically established, safe imaging of diffusion tensor imaging and cerebral blood flow at baseline, during a continuous intravenous infusion of dexmedetomidine at doses designed to produce anesthesia-induced unconsciousness to simulate natural sleep, and again on return to wakefulness. They must be able to pass the standard MRI safety assessment (e.g., no metallic metal clips or implants or any other contraindications to undergoing an MRI).